1. Field of the Invention
The presented invention relates generally to devices for the exploration of luminal cavities. One such device example is an endoscope, which can be used to explore body passages. Such passages typically include, but are not limited to, the GI tract, the pulmonary and gynecological systems, urological tracts, and the coronary vasculature. One application is directed towards the exploration of the lower part of the GI tract, for example the large intestine or colon.
2. Description of the Related Art
Colonoscopy is a diagnostic and sometimes therapeutic procedure used in the prevention, diagnosis and treatment of colon cancer, among other pathologies. With colonoscopy, polyps can be harvested before they metastasize and spread. With regular colonoscopies, the incidence of colon cancer can be substantially reduced.
The anus can provide entry into the colon for a colonoscopy. The colon extends from the rectum to the cecum and has sigmoid, descending, transverse and ascending portions. The sigmoid colon is the s-shaped portion of the colon between the descending colon and the rectum.
Colonoscopy typically involves the anal insertion of a semi-flexible shaft. To typically navigate the colon, the forward few inches of tip are flexed or articulated as the shaft is alternately pushed, pulled, and twisted in a highly skill-based attempt to advance to the end of the colon: the cecum. The medical professional imparts these motions in close proximity to the anus, where the device enters. Tip flexure has typically been accomplished by rotating wheels one that controls cables that move the tip right-left, and one that controls cables that move the tip up-down.
Colonoscopes typically utilize various conduits or channels. The conduits or channels often contain elements that enable vision (e.g., fiber optics, CCD cameras, CMOS camera chips) and lighting (e.g., fiber optic light sources, high power LEDs (Light Emitting Diodes)). They have conduits that provide suction or pressurization, fluid irrigation, the delivery of instruments (e.g., for cutting, coagulation, polyp removal, tissue sampling) and lens cleaning elements (typically a right angle orifice that exits near the camera, such that a fluid flush provides a cleansing wash).
Colonoscopes include articulating sections at their tip, which allow the user to position the tip. These articulating sections have rigid link bodies that rotate relative to each other through the use of pins at their connecting joints. As tensile cables pull from the periphery of the articulating sections, they impart torques, which rotate the link sections on their pins, articulating the tip section. The links are usually rotated by two or four tensile cables.
Typical commercially available colonoscopes are currently reusable. However, as disposable and other lower-cost colonoscopes are developed, these articulatable sections are no longer practical. Their high part count creates total costs that are exorbitant for a lower cost, disposable device. The pivot pins can also fall out, which can create a patient danger. Their design geometries, while suited for long life, high cost, high strength metals elements, don't readily suit themselves to the design goals of lower-cost and more readily mass-produced parts.
Suction can be utilized to remove debris or fluid. The colon can be pressurized to reconfigure the colon into an expanded cross-section to enhance visualization.
During advancement of the colonoscope through the colon, landmarks are noted and an attempt is made to visualize a significant portion of the colon's inside wall. Therapeutic actions can occur at any time, but are typically performed during withdrawal.
Navigating the long, small diameter colonoscope shaft in compression through the colon—a circuitous route with highly irregular anatomy—can be very difficult. Studies have shown a learning curve for doctors performing colonoscopies of greater than two-hundred cases. Even with the achievement of such a practice milestone, the cecum is often not reached, thereby denying the patient the potential for a full diagnosis.
During colonoscopy, significant patient pain can result. This is typically not the result of colon wall contact or of anal entry. The primary cause of pain is thought to be stretching and gross distortion of the mesocolon (the mesentery that attaches the colon to other internal organs). This is commonly referred to as ‘looping’ and is a result of trying to push a long, small diameter shaft in compression as the clinician attempts to navigate a torturous colon. While attempting to advance the tip by pushing on the scope, often all that occurs is that intermediate locations are significantly stretched and grossly distorted. Due to this pain, various forms of anesthesia are typically given to the patient. Anesthesia delivery results in the direct cost of the anesthesia, the cost to professionally administer, the costs associated with the capital equipment and its facility layouts, and the costs associated with longer procedure time (e.g., prep, aesthesia administration, post-procedure monitoring, and the need to have someone else drive the patient home). It has been estimated that forty percent of the cost of a colonoscopy can be attributed to the procedure's need for anesthesia.
Cleaning of colonoscopes is also an issue. Cleaning is time consuming, and lack of cleaning can result in disease transmission. Cleaning can utilize noxious chemicals and requires back-up scopes (some in use while others being cleaned). Cleaning also creates significant wear-and-tear of the device, which can lead to the need for more servicing.
It would therefore be desirable to create a system that is less painful—possibly not even requiring anesthesia—is significantly easier to use, and does not require cleaning.
Everting tube systems have been proposed for use as colonoscopes. However, multiple challenges exist for everting systems. One typical challenge is the differential speed between the center lumen and the tip. For example, as the typical everting tube is advanced, the center lumen of the colonoscope advances 2″ for every 1″ of eversion front advancement. When the center advances it moves only itself, whereas tip movement advances material on both sides. Because there is this dual wall material requirement for tip advancement, two times as much material is required, so it inherently must travel at half the rate.
Anything that is in the center of the typical everting tube is ‘pressure clamped,’ as the tube's inner diameter collapses to no cross sectional area as the tube is pressurized. This can make it difficult to try to solve the 2:1 problem in a typical everting tube by sliding elements in the inner diameter or central region.
This 2:1 advancement issue and the pressure clamping can make it difficult to locate traditional colonoscope tip elements at the everting tip's leading edge. Given that the tube is often long and pressurized, it therefore often precludes the ability to create a functioning center working channel.
Another issue is internal drag. Material (e.g., tube wall) fed to the tip can cause increased capstan drag, for, example the overall system advance force can be retarded to the point of stopping extension.
Optimal material selection is a highly significant challenge. The desired structure must have a rare combination of features: softness, strength, radial stiffness, low thickness, freedom from leaks, flex-crack resistance, puncture resistance, appropriate coefficient of friction, the potential for modifiable geometry as a function of length, and appropriate manufacturability and cost. Monolithic materials have proven insufficient at providing the variety of requisite specifications.
It can be difficult to create a system that is of adequately low stiffness. Larger diameters create higher propulsive forces, but they also do not typically readily conform to the colon in a lumen-centric manner and can be overly stiff.
Historically, several solutions have been suggested. One involves periodically depressurizing the system then withdrawing elements so that their leading edges match. This is time consuming and creates an undesirably non-continuous and geometrically interrupted procedure. It is also very difficult to create ‘correct’ undesirable relative motion to a deflated structure that essentially is no longer a structure. Another approach involves driving the inner lumen (typically with a special, thicker, anti-buckle wall). Because it is driven in compression rather than through pressure, the everting front can be inflated to a lower pressure such that its pressure clamping forces are less significant. This approach, augmented by the significant infusion of liberal amounts of interluminal lubricants, should enable advance. However, it has yet to be commercialized, it is very complicated, creates an undesirably larger diameter instrument, has lubrication leakage issues, and breaks down at longer advance lengths.
Additionally, colonoscopic devices have found it notably challenging to create methods to steer through torturous geometries, particularly without undue colon wall stresses and subsequent mesocolon stretch. Steering kinematics have been an ongoing challenge—certainly for existing colonoscopes (which result in ‘looping’), but also to more effective next-generation devices.
Numerous driven tubes have been proposed for colonoscopy. Some utilize tube inlaid elements driven in compression. Others utilize tubes that are pressure driven, with their tubes being of multiple varieties, including the bellows variety, or everting types, or other stored material varieties, including scrunch, fold, or spooled versions.
The systems proposed to-date have geometries that create suboptimal steering efficacies. When a tube section's leading edge then has a steering section more distal, with typically a camera, lighting source, and working channel exit at the tip, the steering is less than effective when going around a corner: a situation is created in which the tip is retroflexed and is pointing in one desired direction of advance, but the system's advance is in an exactly opposite direction. The driven section presumes a vector—typically an axial manner—with the steering tip only having efficacy as it relates to its interaction with luminal walls. In a colonoscopy, this wall interaction is undesirable—it creates unnecessary wall stress and trauma, and can be a significant contributor to gross wall distortion, known as looping.
It would therefore be desirable to have system designs that enable more lumen-centric steering as the unit is advanced through colon curvature. Other improvements are also desired.